This SCS-C02 practice question tests your understanding of infrastructure security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security engineer is designing a network architecture for a web application that must be highly available and secure. The application uses an Application Load Balancer (ALB) in front of EC2 instances. Which architecture meets these requirements?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Place the ALB in public subnets and EC2 instances in private subnets across two Availability Zones.
Placing ALB in public subnets and EC2 instances in private subnets provides security (instances not directly exposed) and high availability across AZs. Option C is correct. All in public (A) exposes instances. All in private (B) blocks internet traffic. ALB in private (D) cannot receive internet traffic.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Place both the ALB and EC2 instances in private subnets across two Availability Zones.
Why it's wrong here
ALB cannot receive internet traffic in private subnet.
✗
Place the ALB in private subnets and EC2 instances in public subnets across two Availability Zones.
Why it's wrong here
ALB cannot receive internet traffic, instances exposed.
✓
Place the ALB in public subnets and EC2 instances in private subnets across two Availability Zones.
Why this is correct
ALB handles internet traffic, instances are protected.
Place both the ALB and EC2 instances in public subnets across two Availability Zones.
Why it's wrong here
EC2 instances in public subnets are directly exposed.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Place the ALB in public subnets and EC2 instances in private subnets across two Availability Zones. — Placing ALB in public subnets and EC2 instances in private subnets provides security (instances not directly exposed) and high availability across AZs. Option C is correct. All in public (A) exposes instances. All in private (B) blocks internet traffic. ALB in private (D) cannot receive internet traffic.
What should I do if I get this SCS-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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